Cacti are evolving shockingly fast and scientists just learned why

Cacti are famous for growing slowly, but scientists have discovered that these desert plants are actually evolving at an impressive pace. New research shows that cacti are remarkably quick at forming entirely new species, revealing that deserts are far more dynamic than they may seem.

For decades, biologists believed that pollinators and highly specialized flowers were the main forces behind the development of new plant species. However, researchers at the University of Reading found that cacti follow a different pattern. Instead of flower size or pollinator type driving diversification, the key factor appears to be how rapidly cactus flowers change shape over time.

Rapid Flower Evolution in Cacti

The research team analyzed flower length data from more than 750 cactus species. Flower sizes varied dramatically, ranging from tiny blooms measuring just 2mm to giant flowers reaching 37cm, representing a 185-fold difference in size.

Even with such enormous variation, flower length showed almost no connection to how quickly new cactus species emerged. What did stand out was the speed of floral evolution. Cactus species whose flowers changed shape most rapidly were also far more likely to branch off into new species. Researchers found this pattern consistently across both recent and ancient evolutionary history.

The findings, published in Biology Letters, challenge ideas that date back to Charles Darwin. Darwin's work on orchids suggested that highly specialized flower structures played a major role in the formation of new species.

Jamie Thompson, lead author at the University of Reading, said: "People may think of cacti as tough, slow-growing plants, but our research shows that the cactus family is one of the fastest-evolving plant groups on Earth. Knowing how fast cacti evolve reveals that deserts, often seen as harsh and unchanging, are actually hotbeds of rapid natural change.

"We expected cacti with longer, more specialized flowers to be the ones creating the most new species. Instead, flower size made almost no difference. What matters is how quickly flowers change shape. Cacti whose flowers evolve rapidly are far more likely to split into new species than those whose flowers stay the same, however elaborate they are.

"This result has real implications for conservation. Since flower evolution has helped generate cactus species over millions of years, evolutionary pace should become part of conservation efforts. Although being able to rapidly evolve does not guarantee resilience, especially as the planet is changing faster than most cacti can keep up, it could help predict which species need the most help. Rather than searching for a single trait that predicts which cacti are most at risk, conservationists may need to look at how fast a species is evolving instead."

Mapping the Cactus Family Tree

Cacti include roughly 1,850 known species and rank among the fastest-diversifying plant groups on Earth. Over the last 20 to 35 million years, they have spread widely throughout the Americas.

The study also relied on a newly developed Open Access database called CactEcoDB. Created by Jamie Thompson and ten coauthors from three continents, including six researchers from the University of Reading, the database combines seven years of research on cactus traits, habitats, and evolutionary relationships.

The resource was published in Nature Scientific Data and is expected to help scientists better understand cactus biodiversity and conservation challenges. With nearly one-third of cactus species currently threatened with extinction, researchers say the database will provide an important tool for studying how these plants may respond to climate change in the future.